1 files changed, 56 insertions, 0 deletions
diff --git a/tests/rayleigh.py b/tests/rayleigh.py
new file mode 100644
index 0000000..4394ada
--- /dev/null
+++ b/tests/rayleigh.py
@@ -0,0 +1,56 @@
+import unittest
+import numpy as np
+
+from chroma.geometry import Solid, Geometry
+from chroma.make import box
+from chroma.sim import Simulation
+from chroma.optics import water_wcsim
+from chroma.event import Photons
+import histogram
+from histogram.root import rootify
+import ROOT
+ROOT.gROOT.SetBatch(1)
+
+class TestRayleigh(unittest.TestCase):
+    def setUp(self):
+        self.cube = Geometry()
+        self.cube.add_solid(Solid(box(100,100,100), water_wcsim, water_wcsim))
+        self.cube.pmtids = [0]
+        self.sim = Simulation(self.cube, water_wcsim, bvh_bits=4, geant4_processes=0,
+                              use_cache=False)
+        nphotons = 100000
+        positions = np.tile([0,0,0], (nphotons,1)).astype(np.float32)
+        directions = np.tile([0,0,1], (nphotons,1)).astype(np.float32)
+        polarizations = np.zeros_like(positions)
+        phi = np.random.uniform(0, 2*np.pi, nphotons).astype(np.float32)
+        polarizations[:,0] = np.cos(phi)
+        polarizations[:,1] = np.sin(phi)
+        times = np.zeros(nphotons, dtype=np.float32)
+        wavelengths = np.empty(nphotons, np.float32)
+        wavelengths.fill(400.0)
+
+        self.photons = Photons(positions=positions, directions=directions, polarizations=polarizations,
+                               times=times, wavelengths=wavelengths)
+
+    def testAngularDistributionPolarized(self):
+        # Fully polarized photons
+        self.photons.polarizations[:] = [1.0, 0.0, 0.0]
+
+        photon_stop = self.sim.propagate_photons(self.photons, max_steps=1)
+        aborted = (photon_stop.histories & (1 << 31)) > 0
+        self.assertFalse(aborted.any())
+
+        # Compute the dot product between initial and final directions
+        rayleigh_scatters = (photon_stop.histories & (1 << 4)) > 0
+        cos_scatter = (self.photons.directions[rayleigh_scatters] * photon_stop.directions[rayleigh_scatters]).sum(axis=1)
+        theta_scatter = np.arccos(cos_scatter)
+        h = histogram.Histogram(bins=100, range=(0, np.pi))
+        h.fill(theta_scatter)
+        h = rootify(h)
+
+        # The functional form for polarized light should be (1 + \cos^2 \theta)\sin \theta
+        # according to GEANT4 physics reference manual
+        f = ROOT.TF1("pol_func", "[0]*(1+cos(x)**2)*sin(x)", 0, np.pi)
+        h.Fit(f)
+        self.assertGreater(f.GetProb(), 1e-3)
+